The wind turbine industry, both land-based and off-shore, has extended into an economic scaling business, where larger blade systems and larger output have lowered the installed cost per kilowatt/megawatt output. Where typical outputs of 1.5 MW/single turbine installations were common in the 1990s and early 2000s, the industry is pushing into the area of 5.0+MW/single wind turbine installations today. The ability to make blades nearly 265 feet in length, and longer, will require towers in excess of 300 feet in height. This will additionally have the rotor thrusts approaching as high as 220,000 lbs, resulting in base bending moments in excess of 67 million ft.-lbs. Needless to say, the steel pole structure conceptually designed by the Department of Energy (DOE) National Renewable Energy Laboratory (NREL) Technical Report NREL/TP-500-38060, February 2009, “Definition of a 5-MW Reference Wind Turbine for Off-Shore System Development” is a very significant steel pole structure at 347,460 kg in weight, and 87.6 meters in height above ground with a base diameter greater than 8 meters, and having a wall thickness of greater than 5 cm.
The challenges of such a pole are numerous. Extremely large sections of the steel plate, rolled into the correct diameter must be shipped to an installation site in partial sections, and then must be welded and assembled at site, requiring many days of on-site fabrication, with large equipment. Transportation limits by road on width and weight drastically affect the size of steel sections that can be moved to a site. This is because the sections of a steel tower/pole that can be shipped are limited by truck standards (with wide-load-restrictions and weight restrictions per axle). As larger and larger wind turbine rotors are designed, at taller and taller heights, this issue will only become more problematic.
Today, wind turbine structures can represent at least ⅓rd the cost of the entire installed system. A need exists to provide larger tower/pole structures at a lower installed cost.